The proposed studies attempt to clarify on a molecular level the structure _ function relationship in the vicinity of the active site of the lignin peroxidase enzymes and to compare and contrast these with other peroxidases. The local structure of the active site in the intermediate states formed in the H 2O2 dependent primary reactions of lignin peroxidase and other peroxidases will be investigated using x-ray absorption spectroscopy and a specially designed rapid freeze quench apparatus with simultaneous monitoring of optical absorption. Comparison of these data for the various peroxidases and isoenzymes offers a unique approach to identify the structural basis for reactivity and substrate specificity and establish a structure based mechanism for these potentially useful waste degrading enzymes.